Your muscles are made of 2 different types of fibers. Find out what they are, what your personal fiber make-up is and how to train for maximum results.

Knowing your personal muscle fiber make-up can be an
invaluable aid when it comes to properly targeting your
training program. If you're working your muscles in the
wrong way, you'll be cheating yourself out of hard-earned
results.

Every muscle in your body is made up of a bundle of small
fibers. In each bundle, you have two main types of fibers:
slow twitch and fast twitch. I will explain exactly what
these are in a moment. The percentages of these different
fiber types that your muscles are made of can help you
determine exactly how you should train each particular
muscle group in your body.

The Different Muscle Fibers

Slow Twitch:
These are also known as Type 1 or red muscle
fibers. They are responsible for long-duration, low
intensity activity such as walking or any other aerobic
activity.

Fast Twitch:
These are known as Type 2 or white muscle fibers
(divided further into A and B). They are responsible for
short-duration, high intensity activity. Type 2B fibers are
built for explosive, very short-duration activity such as
Olympic lifts. Type 2A fibers are designed for short-to-
moderate duration, moderate-to-high intensity work, as is
seen in most weight training activities.

By looking at elite athletes in different sports, you can see
extreme examples of each make-up of muscle fiber. At the
slow twitch end is the endurance athlete, such as the
marathon runner.

These athletes can have up to 80% or more
of slow twitch muscle fibers in their bodies, making them
extremely efficient over long distances. At the fast twitch
end is the sprinter. World-class sprinters can have up to
80% or more of fast twitch muscle fibers in their body,
making them extremely fast, strong and powerful but with
limited endurance.

How To Find Your Muscle Fiber Type

To find the predominant fiber type in a particular muscle in
your body, we need to test the repetition limits of a muscle
compared to its maximum strength. Keep in mind, these
limits can be altered by your training and are, therefore,
just rough estimates.

First, determine your one rep max (known as the 1 RM) for an
isolation exercise for that muscle group, e.g. the dumbell
curl. Find the weight you can only do one rep with. You
want to use an isolation exercise because any exercise that
uses any other muscle groups will skew the results.

Once you've figured out your one rep max, take a weight that
is 80% of it (multiply your max weight by 0.8 to get this)
and do as many reps as possible with it.

If you can do only 4 to 7 reps with 80% of your 1 RM, you
have mostly fast twitch fibers in that muscle.

The reason you will only be able to do 4 to 7 reps with
80% of your 1 RM is that fast twitch muscle fibers are
strong but don't have great endurance. You will be able
to lift more weight but you be able to do as many reps
with it.

The ability to get approximately ten reps with 80% of
your 1 RM is the typical fiber-type mix for a muscle.
This works out to about a 50/50 split between fiber types.

If you can do 12 to 15 or more reps with 80% of your 1 RM,
your fiber make-up is probably mostly slow twitch fibers.

Slow-twitch fibers are not as strong but have excellent
endurance. This means you won't be able to lift quite as
much but you'll be able to do a lot more reps with it.

Repeat this procedure for each muscle group you wish to
determine a type for (it will vary from muscle to muscle).
By knowing what type of muscle fibers you have, you can
tailor your training towards developing them to their
maximum potential.

Though there are always differences in individuals, there
are some general similarities in fiber types in muscle
groups from person to person.

For example, in most people, the outer, visible muscle of
the calf (the gastrocnemius) is primarily made of slow
twitch fibers while the soleus (which lies underneath the
gastrocnemius) has a higher percentage of fast twitch fibers.

Two more examples of this similarity between people include
the abdominals and the hamstrings. These two muscle groups
are both generally made primarily of fast twitch fibers.

How To Train Your Muscle Fiber Type

When you're training with weights, your goal is to work as
many muscle fibers as possible. Affecting more muscle
fibers means greater gains in strength and muscle mass.

If your fibers in a particular muscle consist primarily of
slow twitch fibers, in order to affect the greatest number
of those muscle fibers, you'll need to train that muscle
with higher reps, shorter rest periods and higher volume.
This is because they take longer to fatigue, they recover
quickly and they require more work to maximize growth.

Unfortunately, slow twitch muscle fibers are limited in
their potential for growth so even if a muscle group is
primarily slow twitch, you should definitely include some
lower rep training to maximize the fast twitch fibers you've
got in that muscle.

If you find you have a hard time gaining size in a particular
muscle, it could be because it has a predominance of slow
twitch muscle fibers. Higher reps (e.g. 12 to 15 reps),
higher volume (more sets) and shorter rest periods (30
seconds to a minute between sets) can help you to maximize
those muscles.

This doesn't mean you should use light
weight, though. You should still strive to use weights that
are as heavy as possible that will cause you to reach failure
in those higher rep ranges. If you don't use heavy weights,
you won't give your muscles a reason to grow.

If your fibers in a particular muscle group consist primarily
of fast twitch muscle fibers, you're one of the lucky ones.
You'll have a much easier time building mass in that muscle -
fast twitch muscle fibers have greater potential for size
than slow twitch. The more fast twitch fibers you've got,
the greater your ultimate muscle size can be. These muscles
are most likely your strongest and quickest to develop.

To maximize your muscles with fast twitch fibers, you'll
need to train with low to moderate reps (e.g. 4 to 8 reps),
rest periods of around 1 to 2 minutes and a moderate
training volume (too much volume will compromise recovery).

If your muscles have a fairly even mix of fibers, you can
evenly divide your training between focusing on the lower-rep,
fast twitch fiber training and the higher-rep, slow twitch
fiber training. This will help you to develop all the
fibers in your muscles, maximizing your ultimate development.

Conclusion

Training your muscles according to their fiber type makes
sense. It will help you to get better results from your
training by allowing you to more specifically target your
training according to the exact specifications of your
muscles.

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